In recent years, research has been done to commercialize transport machines that use hydrogen, natural gas or the like as its driving energy. Such commercialization requires establishment of a utilization environment where such gases under high pressure can be stored and transported. At the same times, high-strength materials used in these applications that have tensile strengths higher than 800 MPa have been developed and their applications have been considered.
WO 2004/083476, WO 2004/083477 and WO 2004/110695 propose increasing Mn to increase the solubility of N and including V or including a combination of V and Nb to take advantage of solute strengthening of N and precipitation strengthening of nitride to provide an austenitic stainless steel with increased strength.
When a high-strength austenitic steel is used as a structure, parts made therefrom must be welded together. To provide sufficient performance in use, the welded portion is required to have a strength substantially equal to that of the base material. WO 2004/110695, JP Hei5(1993)-192785 and JP 2010-227949 propose actively utilizing Al, Ti and Nb to provide a welding material and weld metal having a tensile strength exceeding 800 MPa.
These welding materials and weld metals provided by using these welding materials must be subjected to heat treatment after welding in order to provide high strength. A prolonged heat treatment after welding means a limitation in manufacturing and may cause an increase in manufacturing costs.
WO 2013/005570 proposes taking advantage of solute strengthening of welded metal by N to provide an austenitic-steel welded joint having high strength and good hydrogen embrittlement resistance without performing heat treatment after welding.